1. Field of the Invention
This invention relates to a computer-implemented system for second language learning and more specifically to augmenting such systems with single-trial measurements of a learner's brain response via electroencephalography (EEG) to the presentation of learning materials.
2. Description of the Related Art
Language-learning systems provide effective and non-traditional approaches for learners to learn a second language. Commercially available systems include Tell Me More®, Transparent Language® and Rosetta Stone® are in widespread use by organizations and individuals alike. These systems assess a learner's mastery of different language skills via oral or typed responses to isolate difficulties and adjust the lesson plans accordingly.
Rosetta Stone teaches definitions of words, grammatical distinctions, and formal structures by use of discrete lessons that each introduce or reinforce new language concepts. With each piece of new content, the learner progresses through a sequence of skills to work towards mastery. These skills include the written and audible comprehension of the new word or feature, pronouncing it correctly, and producing it both textually and vocally. The learner is assessed on each of these skills, so that the learner's difficulties can be isolated and more focused practice can be recommended. For example, a learner may pass the exercise that assesses their comprehension of a new vocabulary set, but may fail the exercise that assesses their ability to produce the new content. In this case, Rosetta Stone would recommend that the user repeat the failed exercise. Exercises vary between emphasizing the semantic content of an utterance (meaning) and isolating its syntactic features (rules for composition of words into phrases or sentences). Based on the learner's performance, it is therefore possible to determine whether their difficulty comes from comprehension of new vocabulary or a failure to grasp a new formal or grammatical feature. Rosetta Stone consists of hundreds of screens of content, each consisting of multiple images and various combinations of photo, text and audio stimuli that elicit a response from the learner indicating the their comprehension or correct utilization of a given linguistic feature (e.g., a vocabulary word, a grammatical structure).
Much of the academic research into the neuroscience of how language learning appears as brain activity via electroencephalography (EEG) has focused on Event-Related Potentials (ERP) associated with the processing of semantic and syntactic anomalies. An ERP is a measured brain response that is the result of a thought or perception that can be linked to an event. More formally, it is any stereotyped electrophysiological response to a stimulus. While evoked potentials reflect the processing of the physical stimulus, event-related potentials are caused by the brain processes that might involve perception, memory, expectation, attention, or changes in the mental state, among others. Though some ERP components in language learning are referred to with acronyms (e.g., early left anterior negativity—ELAN), most components are referred to by a preceding letter indicating polarity followed by the typical latency in milliseconds. Thus, the N400 ERP component is described as a negative voltage deflection occurring approximately 400 ms after stimulus onset, whereas the P600 component describes a positive voltage deflection 600 ms after stimulus onset. The stated latencies for ERP components are often quite variable; for example, the N400 component may exhibit latency between 300 ms-500 ms.
In native speakers, semantic anomalies elicit a negative waveform (N400) that peaks at 400 ms after an anomalous word [cf. Kutas & Van Petten 94]. N400 has also been observed for case-marking errors having thematic content in German [Friederici 04]. Left Anterior Negativity (LAN) waveforms have been observed 150-200 ms after the appearance of violation of local phrase structure, such as subject-verb mismatch. [Friederici 95] Late Centroparietal Positivity (P600) appears to arise in situations involving syntactic ambiguity, syntactic complexity and phrase structure violations [Osterhout & Holcomb, 1992; Friederici 04]. fMRI activation foci have been identified for syntactic violations, sentence processing, and syntactic memory in a number of studies [Friederici 04].
Several studies on second language learning demonstrate the appearance of N400 and P600 as markers of emerging language skill. N400 begins to appear in detection of non-words by adult French learners after only 14 hours of instruction [McLaughlin 04]. N400 responses to unusual word/word combinations (word followed by an unrelated word) begin to appear after approximately 62 hours of instruction. Discrimination between well-formed and ill-formed sentences in French elicits an N400 response (P600 is expected for native speakers) after 1 month of instruction. By 4 months of instruction, the N400 effect begins to disappear and is replaced by P600 [Ousterhout 04]. The magnitude of N400 has been hypothesized to reflect the difficulty of integrating multiple linguistic cues [Holcombe, 93]. N400 responses are present in beginning readers (L1) even for ordinary, error-free text [Cock & Holcombe, 2006]. These ERP markers are detected using grand averaging schemes over many trials to detect the emerging language skills.